In a subset of patients with Alzheimer's Disease (AD), perceptual disturbances dominate the clinical picture from the outset. These disturbances, which are often profound and disabling, are of interest from a theoretical as well as a clinical perspective. The primary purpose of the proposed research is to further our understanding of these disorders in terms of the disruption of specific visual processing components. The perceptual deficits will be characterized using neuropsychological tests, and the integrity of processing components will be assessed by means of experimental paradigms derived from perceptual studies of normals. Specific processing stages to be investigated include "pre-attentive" and "attention-requiring" processes in early visual processing; deployment of the "spotlight" of selective attention; the "visual analog representation"; and the "visual buffer" or short-term visual memory system. Data from these experiments are expected not only to help characterize the visual processing impairment associated with AD but also to provide evidence bearing on the adequacy of current information processing models of human vision. In addition, by correlating the site(s) of brain dysfunction as determined by Single Photon Emission Computed Tomography (SPECT) with data assessing the integrity of visual processing components, these studies will contribute to the understanding of the anatomic substrates of human visual perception. A series of psychophysical investigations will be performed to determine the extent to which the processing deficits exhibited by patients with AD reflect impairments in magnocellular and parvocellular visual systems. The data from these studies are also expected to have significant clinical implications. By clarifying the nature of these visual disturbances it should be possible to provide better guidance for caretakers and others involved in the management of these patients. The data will also contribute to the on-going effort to generate a behaviorally meaningful typology of patients with AD.